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NVD / CVE Program· CNA Google

CVE-2021-22555: Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACE

HighCVSS 7.8 · v3.1KEVWeaponized Fix available

Noroxi assessment

Priority: Now (action score 85/100)

  • CISA has confirmed exploitation in the wild (Oct 6, 2025). Remediation deadline for US federal agencies: Oct 27, 2025.
  • A ready-made attack module is public (Metasploit); exploiting it takes no special expertise.
  • Probability of exploitation in the next 30 days: 78.6% (FIRST EPSS); higher than 99.5% of all records.
  • Someone with local access to the system can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: kernel-tools-libs-devel (AlmaLinux:8) 4.18.0-305.12.1.el8_4; linux (Debian:12) 5.10.38-1; kernel-debug (openSUSE:Leap 15.2) 5.3.18-lp152.84.1.
  • Mentioned 2 times in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Patch today or shut off access. Upgrade to kernel-tools-libs-devel (AlmaLinux:8) 4.18.0-305.12.1.el8_4; linux (Debian:12) 5.10.38-1; kernel-debug (openSUSE:Leap 15.2) 5.3.18-lp152.84.1 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · CISA KEV · FIRST EPSS

A heap out-of-bounds write affecting Linux since v2.6.19-rc1 was discovered in net/netfilter/x_tables.c. This allows an attacker to gain privileges or cause a DoS (via heap memory corruption) through user name space

Published
Jul 7, 2021
Updated
Oct 13, 2026
EPSS
78.6% · 99th percentile

Report tools

JSON

Action score

85

Now

Patch today or shut off access.

CVSS
31 / 40 · 7.8 / 10
CISA KEV
30 / 30 · Listed
EPSS
24 / 30 · 78.6%

CISA SSVC decision

Exploitation
active
Automatable
no
Technical impact
total

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
7.8
CNA · Google
8.3
0.5 point gap

CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Actively exploited in the wild

CISA added this to its Known Exploited Vulnerabilities catalog on Oct 6, 2025. That signals real attacks, not theory.

Remediation deadline for US federal agencies: Oct 27, 2025.

Get told when this record changes

  • In CISA KEV: exploitation in the wild confirmed
  • Weaponized exploit exists
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2021-22555

When you'll hear from us

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  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
linuxlinux kernel
netappc400 firmware
netappc400
netappc250 firmware
netappc250
netapph410c firmware
netapph410c
netapph300s firmware
netapph300s
netapph500s firmware
netapph500s
netapph700s firmware

and 24 more

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Google). Independent of NVD's CPE analysis and usually ahead of it.

  • n/a Linux Kernel

    • 2.6.19-rc1 and later · before unspecifiedaffected
Affected versions · NVD (20)

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • broadcom fabric operating systemall versions
  • linux linux kernel4.20 and later · before 5.4.113
  • linux linux kernel4.5 and later · before 4.9.267
  • linux linux kernel4.10 and later · before 4.14.231
  • linux linux kernel4.15 and later · before 4.19.188
  • linux linux kernel5.5 and later · before 5.10.31
  • linux linux kernel5.11 and later · before 5.12
  • linux linux kernel2.6.19 and later · before 4.4.267
  • netapp aff 500f firmwareall versions
  • netapp aff a250 firmwareall versions
  • netapp aff a400 firmwareall versions
  • netapp c250 firmwareall versions
  • netapp c400 firmwareall versions
  • netapp cloud backupall versions
  • netapp fas 8300 firmwareall versions
  • netapp fas 8700 firmwareall versions
  • netapp h300s firmwareall versions
  • netapp h410c firmwareall versions
  • netapp h410s firmwareall versions
  • netapp h500s firmwareall versions

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
AlmaLinux:8kernel-tools-libs-develbefore 4.18.0-305.12.1.el8_44.18.0-305.12.1.el8_4
Debian:12linuxbefore 5.10.38-15.10.38-1
openSUSE:Leap 15.2kernel-debugbefore 5.3.18-lp152.84.15.3.18-lp152.84.1
openSUSE:Leap 15.2kernel-defaultbefore 5.3.18-lp152.84.15.3.18-lp152.84.1
openSUSE:Leap 15.2kernel-default-basebefore 5.3.18-lp152.84.1.lp152.8.38.15.3.18-lp152.84.1.lp152.8.38.1
openSUSE:Leap 15.2kernel-docsbefore 5.3.18-lp152.84.15.3.18-lp152.84.1
openSUSE:Leap 15.2kernel-kvmsmallbefore 5.3.18-lp152.84.15.3.18-lp152.84.1
openSUSE:Leap 15.2kernel-obs-buildbefore 5.3.18-lp152.84.15.3.18-lp152.84.1
openSUSE:Leap 15.2kernel-obs-qabefore 5.3.18-lp152.84.15.3.18-lp152.84.1
openSUSE:Leap 15.2kernel-preemptbefore 5.3.18-lp152.84.15.3.18-lp152.84.1
openSUSE:Leap 15.2kernel-sourcebefore 5.3.18-lp152.84.15.3.18-lp152.84.1
openSUSE:Leap 15.2kernel-symsbefore 5.3.18-lp152.84.15.3.18-lp152.84.1
openSUSE:Leap 15.3kernel-64kbbefore 5.3.18-59.16.15.3.18-59.16.1
openSUSE:Leap 15.3kernel-azurebefore 5.3.18-38.14.15.3.18-38.14.1
openSUSE:Leap 15.3kernel-debugbefore 4.12.14-197.99.14.12.14-197.99.1
openSUSE:Leap 15.3kernel-debugbefore 5.3.18-59.16.15.3.18-59.16.1
openSUSE:Leap 15.3kernel-defaultbefore 5.3.18-59.16.15.3.18-59.16.1
openSUSE:Leap 15.3kernel-defaultbefore 4.12.14-197.99.14.12.14-197.99.1
openSUSE:Leap 15.3kernel-default-basebefore 5.3.18-59.16.1.18.8.15.3.18-59.16.1.18.8.1
openSUSE:Leap 15.3kernel-docsbefore 5.3.18-59.16.15.3.18-59.16.1
openSUSE:Leap 15.3kernel-kvmsmallbefore 5.3.18-59.16.15.3.18-59.16.1
openSUSE:Leap 15.3kernel-kvmsmallbefore 4.12.14-197.99.14.12.14-197.99.1
openSUSE:Leap 15.3kernel-obs-buildbefore 5.3.18-59.16.15.3.18-59.16.1
openSUSE:Leap 15.3kernel-obs-qabefore 5.3.18-59.16.15.3.18-59.16.1

+96

Same product

linux: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-31431crypto: algif_aead - Revert to operating out-of-placeKEV
    90Now
  • CVE-2022-0847A flaw was found in the way the "flags" member of the new pipe buffer structure was lacking proper initialization in copy_page_to_iter_pipe…KEV
    89Now
  • CVE-2016-5195Race condition in mm/gup.c in the Linux kernel 2.x through 4.x before 4.8.3 allows local users to gain privileges by leveraging incorrect…KEV
    83Now

Published before and after this one in the same product

  • ← EarlierCVE-2021-28691Jun 29, 2021 · Guest triggered use-after-free in Linux xen-netback A malicious or buggy network PV frontend can force Linux netback to disable the…
    31Monitor
  • ← EarlierCVE-2021-35039Jul 6, 2021 · kernel/module.c in the Linux kernel before 5.12.14 mishandles Signature Verification, aka CID-0c18f29aae7c.
    31Monitor
  • Later →CVE-2021-3612Jul 9, 2021 · An out-of-bounds memory write flaw was found in the Linux kernel's joystick devices subsystem in versions before 5.9-rc1, in the way the…
    31Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
almalinux:kernel-tools-libs-devel4.18.0-305.12.1.el8_4 · AlmaLinux:8Package registry (OSV)
debian:linux5.10.38-1 · Debian:12Package registry (OSV)
opensuse:kernel-azure5.3.18-38.14.1 · openSUSE:Leap 15.3Package registry (OSV)
opensuse:kernel-debug5.3.18-lp152.84.1 · openSUSE:Leap 15.2Package registry (OSV)
opensuse:kernel-default5.3.18-lp152.84.1 · openSUSE:Leap 15.2Package registry (OSV)
opensuse:kernel-default-base5.3.18-lp152.84.1.lp152.8.38.1 · openSUSE:Leap 15.2Package registry (OSV)
opensuse:kernel-docs5.3.18-lp152.84.1 · openSUSE:Leap 15.2Package registry (OSV)
opensuse:kernel-kvmsmall5.3.18-lp152.84.1 · openSUSE:Leap 15.2Package registry (OSV)
opensuse:kernel-obs-build5.3.18-lp152.84.1 · openSUSE:Leap 15.2Package registry (OSV)
opensuse:kernel-obs-qa5.3.18-lp152.84.1 · openSUSE:Leap 15.2Package registry (OSV)
opensuse:kernel-preempt5.3.18-lp152.84.1 · openSUSE:Leap 15.2Package registry (OSV)
opensuse:kernel-source5.3.18-lp152.84.1 · openSUSE:Leap 15.2Package registry (OSV)
opensuse:kernel-source-azure5.3.18-38.14.1 · openSUSE:Leap 15.3Package registry (OSV)
opensuse:kernel-syms5.3.18-lp152.84.1 · openSUSE:Leap 15.2Package registry (OSV)
red hat:kpatch-patch-4_18_0-3050:1-4.el8 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:kpatch-patch-4_18_0-305_10_20:1-1.el8_4 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:kpatch-patch-4_18_0-305_10_2-debuginfo0:1-1.el8_4 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:kpatch-patch-4_18_0-305_10_2-debugsource0:1-1.el8_4 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:kpatch-patch-4_18_0-305_3_10:1-3.el8_4 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:kpatch-patch-4_18_0-305_3_1-debuginfo0:1-3.el8_4 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:kpatch-patch-4_18_0-305_3_1-debugsource0:1-3.el8_4 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:kpatch-patch-4_18_0-305_7_10:1-2.el8_4 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:kpatch-patch-4_18_0-305_7_1-debuginfo0:1-2.el8_4 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:kpatch-patch-4_18_0-305_7_1-debugsource0:1-2.el8_4 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:kpatch-patch-4_18_0-305-debuginfo0:1-4.el8 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:kpatch-patch-4_18_0-305-debugsource0:1-4.el8 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
rocky linux:kernel0:4.18.0-305.12.1.el8_4 · Rocky Linux:8Package registry (OSV)
rocky linux:kernel-rt0:4.18.0-305.12.1.rt7.84.el8_4 · Rocky Linux:8Package registry (OSV)
suse:kernel-64kb5.3.18-59.16.1 · SUSE:Linux Enterprise Module for Basesystem 15 SP3Package registry (OSV)
suse:kernel-azure4.12.14-16.65.1 · SUSE:Linux Enterprise Server 12 SP5Package registry (OSV)

+10

Exploit status

Weaponized

A ready exploit tool or active in-the-wild use is known for this vulnerability. This should be your top priority.

Evidence

  • Metasploit module ×1
  • Exploit-DB entry ×1
  • Proof-of-concept repository on GitHub ×13

Noroxi does not host or link to exploit code. Metasploit module names and Nuclei template ids are shown (names, not code); Exploit-DB entries and PoC repositories are given as counts only.

Public exploit evidence
SourceKindDate
Proof-of-concept repository on GitHub13 repositories2021-07-15 → 2026-07-21
Exploit-DB entrylocal2021-07-15
Metasploit moduleexploit/linux/local/netfilter_xtables_heap_oob_write_priv_escNetfilter x_tables Heap OOB Write Privilege Escalationexploit2021-07-07

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

  1. Metasploit-1 d
  2. Published
  3. First PoC+7 d
  4. CISA KEV+1551 d
  5. TodayNov 12, 2026+1954 d

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

All national notices →

Not on record for this CVE: EPSS history · variant or chain candidate · public bounty program.

Technical details

Attack conditions

  • Someone with local access to the system can trigger it.
  • A low-privileged account is enough.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
high · data can be read
Integrity
high · data or configuration can be modified
Availability
high · the service can be disrupted
Attack vector
Local
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
High
Availability impact
High

Weakness class (CWE)

CWE-787 · Out-of-bounds Write

CVSS vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

References

Show all references (3 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records